An ultrasonic diagnostic apparatus performs ultrasonic scanning along an arbitrary cross-sectional plane inside an object by an ultrasonic probe and constructs and displays, for example, a tomographic image on the basis of RF signal frame data obtained by performing reception processing on a reflection echo signal from a living tissue at a cross-sectional position including the cross-sectional plane. Since RF signal frame data here is substantially identical to tomographic image data, the term tomographic image data in the description below conceptually includes RF signal frame data.
Also, it is commonly performed to repeatedly measure RF signal frame data at a single cross-sectional position while pressing an object with an ultrasonic probe, obtain displacements of parts of a living tissue at the cross-sectional position on the basis of two pieces of RF signal frame data different in measurement time (the amount of pressing), and construct an elasticity image indicating the hardness or softness of the living tissue on the basis of obtained displacement frame data (e.g., Patent Literature 1). Elasticity information indicating the hardness or softness of a living tissue is typically a strain or the elastic-modulus of the living tissue. It is, however, well-known that examples of elasticity information include a physical quantity, such as a displacement, correlating with a strain or an elastic-modulus.
Further, it is commonly performed to transmit/receive ultrasonic waves while moving an ultrasonic probe in a short axis direction orthogonal to a direction in which transducers are arranged (a long axis direction), measure respective two-dimensional tomographic images at different cross-sectional positions to generate volume data of the tomographic images, perform volume rendering using the volume data to construct a three-dimensional tomographic image (e.g., a two-dimensional projection image), and display the three-dimensional tomographic image (e.g., Patent Literature 2). In this case, a position sensor which measures the position and tilt of the ultrasonic probe is provided, position information and tilt information are acquired at the same time as transmission/reception of ultrasonic waves, and a plurality of two-dimensional tomographic images are registered in association with three-dimensional coordinates of volume data. With a three-dimensional tomographic image constructed in the above-described manner, information on the extent of a part of interest can be observed from a different angle.
Similarly, the process of constructing and displaying a three-dimensional elasticity image has been proposed in order to intuitively recognize the shape and volume of a hard part or a soft part present in a living tissue (e.g., Patent Literature 3). According to the process, elasticity image volume data composed of a plurality of two-dimensional elasticity images measured by general elasticity image measurement is generated, and a three-dimensional image (e.g., a two-dimensional projection image) is constructed on the basis of the elasticity image volume data. A further improvement in visibility by displaying a three-dimensional elasticity image to be superimposed on, e.g., a three-dimensional tomographic image has also been proposed.